Printer

ABSTRACT

In a printer, an image is formed by discharging a light curing type ink from a recording head on a recording medium and irradiating light from a light emission unit so as to harden the ink. The printer comprises a short arc type discharge lamp in which a pair of electrodes is provided in an electric discharge container so as to face each other a reflector which is provided so as to surround the discharge lamp, which has a concave face which reflect light from the discharge lamp wherein the pair of the electrodes are arranged so that a straight line formed by connecting the pair of electrodes, extends along an optical axis of the reflector, and wherein mercury of 0.08-0.30 mg/mm 3 , rare gas, and halogen is enclosed in the electric discharge container and a distance between electrodes is 0.5-2.0 mm.

CROSS-REFERENCES TO RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2007-210731, filedAug. 13, 2007 including its specification, claims and drawings, isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Described herein is a printer which discharges a light curable ink to arecording medium, and then irradiates light to the ink thereby recordingan image on the recording medium.

BACKGROUND

Since a recording method called an ink jet printing can produce an imagemore simply and cheaply than a gravure printing method, in recent years,such an ink jet printing has been applied to various printing fields,such as special printings, that is, photograph, various printing method,marking, or color filters. In the ink jet recording method, a highquality image can be obtained by combining a printer for controllingdischarge of a fine dot (ink), an ink whose color-reproduction range,durability, adequate accuracy of discharge, etc., is improved, anddedicated paper whose ink absorbency, color-material coloring nature,surface gloss, etc is dramatically improved. These printers can beclassified according to kinds of inks. Among these printers, there is alight curing type ink jet system in which a light curing type inkhardened by light such as ultraviolet rays etc. is used. A light curingtype ink jet system emits a comparatively low odor, and quick-dryingcapability can be chiefly expected even though the dedicated paper isnot used. Moreover, it has been brought to attention since it isrecordable on a recording medium without ink absorbency.

In such an light curing type inkjet printer (hereinafter referred to asa ink jet printer), in addition to the recording head (also referred toas an ink jet, below) from which a fine ink droplet is discharged to arecording medium, a light source which emits light is carried in acarriage of the printer. The carriage is moved while the light source islit above the recording medium, and the light is irradiated to the inkimmediately after the ink directly hits the recording medium, so thatthe ink is hardened (refer to, for example, Laid Open Patent Nos.2005-246955, 2005-103852, and 2005-305742 and “The current situation andlatest topics of the energy line hardened resin technology for paints,”NO. 11/2005, pp 1-20, DIC Technical Review of Dainippon Ink & Chemicals,Inc., Yoichi Abe). In addition, attempts have been made to use such anink jet printer for not only record printing of such an image but alsopatterning of an electronic electrical circuit. In this case, thematerial in form of liquid which is discharged from an ink jet head is amaterial for circuit board formation, such as a light curing type resistink. The base material to which printing (namely, formation of apattern) is performed is a printed circuit board. In a formation of thecircuit pattern with resist ink, drying and curing reaction by light,such as ultraviolet rays, is used as in the record printing of an image.Although there is difference therebetween, in that an ink material whichis discharged from an ink jet head is a resist and an ink, the structureof the ink jet printer apparatus used for the patterning and printing isthe same.

Description of an ink jet printer will be given below, as an example theapparatus which records an image on a base material using a lightcurable ink.

FIG. 8A is a schematic perspective view of a head section of an ink jetprinter. FIG. 8B is a cross sectional view of light emitting units 6 or7 shown in FIG. 8A, taken along a plane perpendicular to the opticalaxis of a lamp. In addition, FIG. 8A shows the light emitting units,wherein the interior thereof can be seen, so that explanation thereofbecomes easy. The ink jet printer 1 has a rod shape guide rail 2, and acarriage 3 is supported by the guide rail 2. The carriage 3 performsback-and-forth movement along the guide rail 2 above the base material(recording medium) 5 by a carriage driving mechanism (not shown). Thedirection is referred to as a direction X, hereinafter. An ink jet head4 in which a nozzle (not shown) for discharging an ink for each colorfor color printing is provided, is mounted in the carriage 3. The lightemitting units 6 and 7 are provided in the both sides of the ink jethead 4 in moving directions of the carriage 3, and the light emittingunits 6 and 7 irradiate ultraviolet rays to the ink which is the liquidmaterial discharged onto the recording medium 5 from the nozzle of theink jet head 4. In addition, a portion which consists of the ink jethead 4 and the light emitting sections 6 and 7 is referred to as a headsection 1 a below.

When printing is performed to the recording medium 5 while the carriage3 moves toward the front side in the direction X of FIG. 8, ink from theink jet head 4 of the head section la is hardened by the light fromlight emitting unit 6. Moreover, when printing is performed to therecording medium 5 while the carriage 3 moves toward the back side inthe direction X of the figure, ink from the ink jet head 4 is hardenedby light from the light emitting unit 7. As a light source which emitslight (ultraviolet rays) of wavelengths required to harden the ink, forexample, a high-pressure mercury lamp and a metal halide lamp, etc. eachof which is a long arc type discharge lamp, are known. As shown in FIG.8B, each of the light emitting units 6 and 7 has a box-like cover member8 which has an opening 20, opening toward the recording-medium 5. A longarc type discharge lamp 90 is arranged, inside this cover member 8,along a direction (hereinafter referred to as a direction Y)perpendicular to the movement direction (the direction X) of thecarriage 3. Each of the discharge lamp 90 is a linear light source, andthe length of a light emission section thereof is approximately equal tothe length (in the direction Y) of the ink jet head 4.

A gutter-like reflector 110 which reflects light (ultraviolet rays)emitted from the lamp 90, is provided in the opposite side of theopening 20 with respect to the lamp 90. As shown in FIG. 8B, thereflector 110 has an ellipse shape in a sectional view thereof, and thedischarge lamp 90 is arranged at the first focal point of the reflector110. Although the light (ultraviolet rays) emitted from the lamp 90 iscondensed by the second focal point of the reflector 110 in a linearshape, direct light from the lamp 90 is also added thereto and isirradiated to the recording medium 5. The recording medium 5 is arrangedso as to pass through a second focal point position of the reflector110, or therenear, and the light condensed by the reflector 110 isirradiated onto the recording medium 5 to which the ink has reached.

As described above, as a light curable ink used for an ink jet printer,the ultraviolet curing type ink which is hardened by so-calledultraviolet rays, is used. And as a light source which emits theultraviolet rays, as described above, the high-pressure mercury lamp orthe metal halide lamp in which heavy metal is enclosed in addition tomercury, is used. Reaction of polymerization initiator contained in theink is started by ultraviolet-rays irradiation, and the ultravioletcuring type ink is hardened. A radical curing type initiator is oftenused as such a polymerization initiator, and it is known thatwavelengths of the light to be absorbed (that is, polymerization isstarted) is 250-400 nanometers (nm) (refer to, for example, “The currentsituation and latest topics of the energy line hardened resin technologyfor paints,” NO. 11/2005, page 1, column 2, lines 12 to page 2, column1, line 5, DIC Technical Review of Dainippon Ink & Chemicals, Inc.).Therefore, it is desirable that, as a light source of the ink jetprinter, many components of light with wavelengths of 250-400 nm becontained in the light emitted.

On the other hand, an ink jet printer is often used for a large-sizedgraphic printing of car exterior display, outside/indoor ornamentdisplay etc. Therefore, as a recording medium, i.e., a base material tobe printed, an acrylics film which is excellent in weather resistance,is often used for the car exterior or outside display. In addition, aPET (polyethylene terephthalate) film which is excellent intransparency, thermal resistance, electric insulation, and chemicalresistance, is also often used for indoor ornament display. Moreover, inaddition to this, polycarbonate (used for a digital video disc), ABSresin, polystyrene (PS), etc. are used as a base material. Each of thebase materials of macromolecule (pi conjugation polymer) having, forexample, a pi covalent bond, such as PET, a polycarbonate, ABS resin,and PS, has an absorption band at approximately 200 nm-300 nm. Moreover,although acrylics is not pi conjugation polymer, the penetrationthreshold wavelength thereof in an ultraviolet range is 280 nm, andlight of the wavelength which is not greater than that, is absorbedtherein. Therefore, when the base material absorbs light with awavelength of 300 nm or less, so that the absorbed light energy ischanged into heat, the temperature of the base material may go up and,as a result, deformation thereof may occur. Therefore, it is desirablethat light with wavelengths of 300 nm or less which such a base materialabsorbs, is not contained in the light emitted from the light source.

However, in light emitted from the high-pressure mercury lamp or themetal halide lamp, which is conventionally used, not only light withwavelengths of 300-400 nm but light with wavelengths of 300 nm or lessis also contained. Therefore, if, in order to shorten curing time ofink, the irradiance of light with wavelengths of 300-400 nm is increasedby increasing electric power of the lamp, the irradiance of the light ofthe wavelengths of 300 nm or less is also increased. Therefore, the basematerial is heated so that there is a problem that deformation tends tooccur.

Insertion of a wavelength cut-off filter is known as a method ofremoving light of a certain wavelength band from light emitted from alamp. A multilayer film deposition filter is known as a filter whichcuts a short wavelength. A multilayer film deposition filter is formedin form of a multilayer consisting of inorganic films whose thickness isadjusted according to wavelengths to be cut. However, since thehigh-pressure mercury lamp or the metal halide lamp which isconventionally used as a light source is a long arc type lamp, diverginglight is emitted from the long arc type lamp. Therefore, even if themultilayer film deposition filter which cuts short wavelength betweenthe lamp and the base material is provided, the light enters the filterat various angles, so that the film thickness of the multilayer filmwhich is formed in the filter seemingly changes depending on incidentangles of the light. Therefore, All the light with wavelengths of 300 nmor less cannot be cut.

SUMMARY

In view of the above, described herein is a printer in which a lightcurable ink is discharged toward a recording medium from a recordinghead, and in which the ink on the recording medium is hardened byemitting light from a light emitting unit, thereby recording an imagethereon, wherein a lamp in which although many components of light withwavelengths of 300-400 nm are contained in light from the light sourcebut light with wavelengths of 300 nm or less is not contained therein,is used, so as not to heat the base material even if electric power ofthe lamp is increased, and not to cause deformation thereof.

As mentioned above, in an ink jet printer which uses light curable ink,it is desirable that the light emitted from the light source does notcontain light with wavelengths of 300 nm or less which a base materialabsorbs.

As a result of examining various matters, it found out that it issuitable that a short arc type ultra-high pressure mercury lamp whosedistance between electrodes is 0.5-2.0 mm, is used as a discharge lampfor the light source, in which a pair of electrodes is arranged in anelectric discharge container so as to face each other, and mercury of0.08-0.30 mg/mm³, rare gas, and halogens is enclosed in an electricdischarge container. In the case of the high-pressure mercury lamp orthe metal halide lamp which is used as a light source of a conventionalink jet printer, although a component of the wavelengths of the range of300-400 nm are contained in light emitted from a lamp, a component ofthe wavelengths of 300 nm or less is also contained. On the other hand,although the component of the wavelengths of the range of 300-400 nm iscontained in light emitted from the ultra-high pressure mercury lampaccording to the present invention, most of the component of wavelengthsof 300 nm or less is not contained.

In addition, although the ultra-high pressure mercury lamp is known as alamp used for a projector, since attention is not paid to the spectraldistribution of the wavelength range of 300 nm or less, there is norecognition that it is suitable to use it as a light source for an inkjet printer.

The present ultra-high pressure mercury lamp is used as a light source,in which a concave reflector arranged so as to surround a lamp isprovided, and a straight line connecting a pair of electrodes of thelamp extends along the optical axis of the reflector.

The optical axis of the reflector is, for example, the same as an axisof the rotation symmetry. The present reflector may have at least 180degrees rotation symmetry (two fold symmetry), and ellipsoid ofrevolution or paraboloid of revolution is often used therefor.

In such a structure, only a component of light reflected on thereflector among components of the light from the lamp is emitted, andthe direct light from the lamp is hardly emitted. For this reason, if amultilayer film deposition mirror which reflects only ultraviolet raysis used as a reflector, even if the light of a visible region to aninfrared region is contained in the light emitted from a lamp, suchlight is not directly irradiated onto a base material (recordingmedium). Moreover, it is possible to prevent the radiant heat generatedby lighting of the discharge lamp from being directly irradiated ontothe base material (recording medium), so that a degree of the influenceof the heat to the base material (recording medium) can be reduced.

In view of the above, in order to solve the problems, in the presentprinter, an image is formed by discharging a light curing type ink froma recording head on a recording medium and irradiating light from alight emission unit so as to harden the ink. The printer comprises ashort arc type discharge lamp in which a pair of electrodes is providedin an electric discharge container so as to face each other, a reflectorwhich is provided so as to surround the discharge lamp, which has aconcave face which reflect light from the discharge lamp, wherein thepair of the electrodes are arranged so that a straight line formed byconnecting the pair of electrodes, extends along an optical axis of thereflector, and wherein mercury of 0.08-0.30 mg/mm³, rare gas, andhalogen is enclosed in the electric discharge container and a distancebetween electrodes is 0.5-2.0 mm. The optical axis may be

The printer may include a mirror which forms light reflected by thereflector so as to be in a linear shape, wherein the discharge lamp isarranged so that the straight line formed by connecting the pair ofelectrodes to be perpendicular to the recording medium.

Also, the printer may include a first mirror which changes a directionof light reflected by the reflector and a second mirror which formslight directed by the first mirror so as to be in a linear shape,wherein the discharge lamp is arranged so that the straight line formedby connecting the pair of electrodes to be parallel to the recordingmedium.

Accordingly, effects set forth below can be acquired.

(1) Since the short arc type ultra-high pressure mercury lamp in whichmercury of 0.08-0.30 mg/mm³, rare gas, and halogen gas is enclosed inthe electric discharge container and the distance between electrodes is0.5-2.0 mm, is used as a light source for the ink jet printer, lightwith wavelengths of 300 nm or less is hardly emitted, and deformationdue to heating of the base material can be prevented.

(2) Since the concave reflector which reflects light from the dischargelamp and is arranged so that the discharge lamp may be surrounded, isprovided and a straight line connecting a pair of electrodes of the lampmay extend along the optical axis of the reflector, among components oflight from the discharge lamp, the light emitting unit emits only lightreflected by the reflector, so that direct light from the lamp is hardlyemitted. For this reason, by using the mirror which reflects onlyultraviolet rays as the reflector, even if the radiant heat and thelight in a range from a visible region to an infrared region, from thelamp is emitted, it is possible to prevent the base material (recordingmedium) from being irradiated directly, so that the degree of theinfluence of heat to the base material (recording medium) can be reducedfurther.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present printer will be apparentfrom the ensuing description, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic cross sectional view of the structure of an inkjet printer according to a first embodiment;

FIG. 2 is a graph showing the radiant efficiency of wavelength band ofan ultra-high pressure mercury lamp according to an embodiment, that ofhigh-pressure mercury lamp, and that of a metal halide lamp of priorart;

FIG. 3 is a graph showing a Deep UV ratio of an ultra-high pressuremercury lamp according to an embodiment, that of a high-pressure mercurylamp, and that of a metal halide lamp of prior art;

FIG. 4 is graph showing a spectral distribution of a range of 250 nm-450nm wavelength of an extra-high pressure mercury lamp according to anembodiment;

FIG. 5 is a graph showing a spectral distribution of a range of 250nm-450 nm wavelengths of a high-pressure mercury lamp of prior art;

FIG. 6 is a graph showing a spectral distribution of a range of 250nm-450 nm wavelengths of a metal halide lamp of prior art;

FIG. 7 is a schematic cross sectional view of the structure of an inkjet printer according to a second embodiment;

FIG. 8A is a schematic view of the structure of a head section of aconventional ink jet printer; and

FIG. 8B is a cross sectional view of a conventional light emitting unit.

DESCRIPTION

The descriptions in the specification are provided for illustrativepurposes only, and are not limiting thereto. An appreciation of variousaspects of the present printer is best gained through a discussion ofvarious examples thereof. The meaning of these terms will be apparent topersons skilled in the relevant arts based on the entirety of theteachings provided herein.

FIG. 1 shows a first embodiment according to the present invention. FIG.1 is a schematic cross sectional view showing the structure of a headsection of an ink jet portion, in which light emitting units, each ofwhich is equipped with an ultra-high pressure mercury lamp, are providedto the head section of the ink jet printer. In addition, althoughdescription of the ink jet printer which is used for an image printingwill be given below as an example, it can be similarly applied to aformation of patterns of, for example, a circuit. The ink jet printeraccording to this embodiment has, for example, the same structure asthat shown in FIGS. 8A and 8B, except that the structure of the lightemitting units is different from those shown in FIG. 8. Namely, the inkjet printer 1 includes the head section 1 a including an ink jet head 4and the two light emitting units 6 and 7, and the head section issupported by a carriage 3. In the ink jet head 4, a nozzle (not shown)which discharges fine droplets of a light curable ink, for example, amaterial in form of liquid, such as an ultraviolet curing type ink, to abase material 5 is provided. The two light emitting units 6 and 7 areprovided in the both sides of this ink jet head 4, and harden an inkwhich reaches the base material 5, by irradiating light of apredetermined wavelength band, for example, ultraviolet rays.

The head section la is supported by the cylindrical guide rail 2provided so as to extend along the base material 5. A driving mechanism(not shown) enables both-way movements in the horizontal directions ofthe figure, above the base material 5 along with the guide rail 2. Forexample, a radical polymerization system ink which contains aradical-polymerizable compound as a polymerizable compound, or acationic polymerization system ink which contains a cationicpolymerizable compound as a polymerizable compound may be used as anultraviolet curing type ink. In addition, when such an ink jet printeris used for pattern formation of, for example, a circuit, a resist inkcontaining a light intensity synthetic compound etc. is used as amaterial in form of liquid which is discharged from the ink jet head.For example, paper, resin, a film, a printed circuit board, etc. can beused as the base material 5. As the resin, PET (polyethyleneterephthalate), ABS, acrylic resin, etc. may be used.

Next, the structure of the light emitting units 6 and 7 is explained.Each of the light emitting unit is equipped with the ultra-high pressuremercury lamp 11 which is a short arc type discharge lamp, and a lightsource section 10 which comprises a reflector 12 for reflecting lightfrom the discharge lamp, wherein light from the discharge lamp 11 isirradiated so that an light emitting area extending in a linear shapemay be formed on a light exposed face. Each of the light emitting units6 and 7 has, for example, an exterior cover 14 having a box shape as awhole, and a light emitting window 14 a which is open (in the basematerial 5 side) at a lower part of FIG. 1. The light source section 10having the ultra-high pressure mercury lamp 11, and the reflector 12which is arranged so as to surround the lamp 11 and which reflects lightemitted from the lamp 11, is provided in the exterior cover 14.Moreover, reflective mirrors 13 for emitting light to the outsidethrough the light emitting window 14 a are arranged, so that the lightfrom the light source section 10 is shaped so as to extend in a linearshape on a light emitting area. The reflector 12 which forms the lightsource section 10 is formed as a parabola mirror which has a reflectivesurface 12 b in a shape of revolution paraboloid whose center is anoptical axis C. A light emitting opening 12 a of the reflector 12 facesthe light emitting window 14 a of the light emitting unit 10, and opensdownward (in the base material 5 side) in FIG. 1. The optical axis C isarranged so as to be perpendicular to the light exposed face (materialface).

While a pair of electrodes is arranged in an electric dischargecontainer of the ultra-high pressure mercury lamp 11 which forms thelight source section 10, in a state where the distance between theelectrodes is set to 0.5-2.0 mm, a predetermined amount of mercury whichis a light-emitting material, and a predetermined amount of rare gas andhalogen which are buffer gas for start-up assistance are enclosed. Here,the enclosure amount of the mercury is 0.08-0.30 mg/mm³. In a statewhere the light emission section (radiant spot of an arc) is located ina focal point Fr of the reflector 12, the lamp 11 is arranged so that astraight line connecting a pair of electrodes may extend along theoptical axis C of the reflector 12. Each of mirrors 13 has the shape ofa long and slender plane, and is arranged so that the longitudinaldirection thereof may extend in the direction of the front and back sideof FIG. 1. The two mirrors 13 are arranged to face each other, and toform the long and slit-like light emitting window 14 a in the front/backdirections of FIG. 1. The light from the lamp 11 becomes parallel lightalong the optical axis C, when the light is reflected by the reflector12 which has the revolution paraboloid reflective surface 12 b, and partof the light is directly emitted from light emitting window 14 a. Theother parts of the light is reflected by the mirrors 13 and is emittedfrom the light emitting window 14 a. On the base material 5, a long andnarrow light emitting area IA extending in the front/back directions ofFIG. 1 is formed.

Here, in the discharge lamp 11, the straight line formed by connectingthe pair of electrodes is located along the optical axis C of thereflector 12. The electrodes are provided at a portion where the openingof the reflector 12 of the discharge lamp 11 faces. For this reason,light which is emitted from the discharge lamp 11 is not directlyirradiated to the light exposed face (material face), so that most ofthe light emitted from the discharge lamp 11 becomes parallel light whenit is reflected on the reflector 12. When as the reflector 12, adeposition mirror which reflects light with short wavelength, buttransmits light with long wavelengths in a range of a visible region toan infrared region which does not contribute curing of the ink isprovided, even if the light with wavelengths of 300 nanometers (nm) orless is emitted from the ultra-high pressure mercury lamp 11, it ispossible to prevent light which is unnecessary for hardening the ink,from being irradiated onto the base material 5, so that it is possibleto prevent the base material 5 from being heated. Furthermore, if afilter which cuts the light with the wavelengths of 300 nm or less isinserted into a light emitting side of the light source section 10, itis possible to further prevent the light with wavelengths of 300 nm orless from being irradiated onto the base material 5.

In the ink jet printer, when the head section 1 a equipped with the inkjet head 4 and the light emitting units 6 and 7, moves above the basematerial 5 in the state where the ultra-high pressure mercury lamp 11 islit, the light from the lamp 11 is formed on the base material 5 so asto be a linear light emitting area extending in a direction(perpendicular to the face of FIG. 1) which is orthogonal to thedirection of movement of the head section 1 a, so that the ultravioletcuring type ink is immediately hardened after reaching the base material5. The curing processing of the ultraviolet curing type ink is explainedin detail, below. In FIG. 1, when printing is performed to the basematerial 5 while the head section 1 a is moved rightward, theultraviolet curing type ink which reaches the base material 5 ishardened by the light irradiated from the light emitting unit 6 locatedin a back side of the head section 6 in the movement direction thereof.On the other hand, when printing is performed to the base material 5while the head section 1 a is moved leftward in FIG. 1, the ultravioletcuring type ink which reaches the base material 5 is hardened by thelight irradiated from the light emitting unit 7 located in a back sideof the head section 6 in the movement direction thereof.

Here, the property of the ultra-high pressure mercury lamp used in theabove embodiments, and that of the high-pressure mercury lamp and themetal halide lamp used in the prior art are compared with each otherbelow. FIGS. 4-6 show the spectral distribution of a wavelength range of250 nm-450 nm of the ultra-high pressure mercury lamp according to theembodiments, that of the high-pressure mercury lamp and that of themetal halide lamp of the prior art, respectively. In these figures, ahorizontal axis shows wavelength (nm) and a vertical axis showsluminescence intensity (relative value). As shown in FIGS. 5 and 6, in acase of the high-pressure mercury lamp or the metal halide lamp which isused as a light source of the conventional ink jet printer, although thecomponent of the wavelength range of 300-400 nm is contained in lightemitted from a lamp, a component of 300 nm or less is also containedtherein. However, as shown in FIG. 4, although the component of thewavelength range of 300-400 nm is contained in light emitted from theultra-high pressure mercury lamp according to the embodiment, most ofthe component of 300 nm or less is not contained therein.

The radiant efficiency of a wavelength band of the ultra-high pressuremercury lamp according to the embodiments, that of the high-pressuremercury lamp of prior art, and that of a metal halide lamp are shown inFIG. 2. FIG. 2 shows what percent of the full wavelength area of lightemitted from the lamp, a component of light in a range of 220 nm-300 nmwavelengths and that in a range of 300 nm-450 nm wavelengths make, whenthe same input electric power is applied to each lamp, based on thespectral distribution shown in FIGS. 4-6. In addition, the amount ofmercury in the high-pressure mercury lamp is 0.03 mg/mm³, and the amountof mercury in the metal halide lamp is 1.7×10⁻⁴ mg/mm³. Although, asshown in this figure, the light in the range of 300 nm-450 nmwavelengths emitted from the metal halide lamp is the most among theselamps, the light in the range of 220 nm-300 nm wavelengths is alsoemitted. On the other hand, even though the ultra-high pressure mercurylamp according to the embodiments hardly emits the light in the range of220 nm-300 nm wavelengths, the light in the range of 300 nm-450 nmwavelengths is emitted more than that from the high-pressure mercurylamp.

FIG. 3 shows a result (Deep UV ratio) which was obtained by dividing avalue of the wavelengths of 220 nm-300 nm by a value of the wavelengthsof 300 nm-450 nm, in an embodiment shown in FIG. 1. This valuerepresents the amount of the light with the wavelengths of 220 nm-300 nmin case where the amount of light with wavelengths of 300 nm-450 nm wasthe same in the lamps which were compared with one another. As shown inthis figure, in the ultra-high pressure mercury lamp according to theembodiments, there was almost no light intensity with the wavelength of220 nm-300 nm, compared with the amount of light with the wavelengths of300 nm-450 nm. Therefore, even if an irradiance with the wavelength of300 nm-450 nm was increased by increasing electric power of the lamp inorder to shorten the processing time for curing ink by light, sincethere was little light with the wavelengths of 300 nm or less emittedfrom the lamp, the base material did not absorb light with wavelengthsof 300 nm or less so that the base material was not heated, whereby itwas possible to prevent the problem of deformation etc.

Although, in the first embodiment shown in FIG. 1, the straight lineconnecting the pair of electrodes of the discharge lamp 11 isperpendicular to the base material (recording medium) 5, in a secondembodiment which is described below, a straight line connecting a pairof electrodes of a discharge lamp 11 is parallel to the base material(recording medium).

FIG. 7 shows a second embodiment. FIG. 7 is a schematic cross sectionalview of the structure of a head section of an ink jet printer havinglight emitting units. The ink jet printer according to this embodimenthas the same structure as that shown in FIG. 1, except that thestructure of the light emitting units is different from that shown inFIG. 1. The ink jet printer 1 includes an ink jet head 4 and the twolight emitting units 6 and 7 which are provided in the both sides ofthis ink jet head 4. The ink jet head 4 and the two light emitting units6 and 7 are supported by the head section 1 a, and the head section 1 ais carried by a carriage 3.

Each of the light emitting units 6 and 7 is equipped with an ultra-highpressure mercury lamp 11 which is a short arc type discharge lamp, and alight source section 10 comprising a reflector 12 which reflects lightfrom the discharge lamp as in the first embodiment, in which light fromthe discharge lamp 11 is irradiated so that the light emitting areaextending in a linear shape is formed on a light exposed face. The lightsource section 10 having the ultra-high pressure mercury lamp 11, andthe reflector 12 which is arranged so as to surround the lamp 11 andwhich reflects light emitted from the lamp 11, is arranged inside theexterior cover 14 of each light emitting unit (6 and 7). The reflector12 is formed as a parabola mirror which has a reflective surface 12 b ina shape of revolution paraboloid whose center is an optical axis C.Moreover, as shown in FIG. 7, when the discharge lamp 11 is horizontallyarranged, a second mirror 15 which reflects light reflected by thereflector 12 is arranged at the incidence side of a mirror 13 whichforms a light emitting window 14 a.

While in an electric discharge container of the ultra-high pressuremercury lamp 11, as mentioned above, a pair of electrodes is arranged soas to face each other at an interval (a distance between electrodes) of0.5-2.0 mm, a predetermined amount of mercury which is a light-emittingmaterial, and a predetermined amount of rare gas and halogen which arebuffer gas for start-up assistance are enclosed. For example, theenclosure amount of the mercury is 0.08-0.30 mg/mm³. As mentioned above,in a state where the light emission section (luminescent spot of an arc)is located at the focal point Fr of the reflector 12, the lamp 12 isarranged so that a straight line connecting a pair of electrodes mayextend along the optical axis C of the reflector 13. These two mirrors13 are arranged to face each other, and to form a long and slit-likelight emitting window 14 a in the front/back directions of FIG. 7. Thelight from the lamp 11 becomes parallel light to the optical axis C whenthe light is reflected by the reflector 12 which has the revolutionparaboloid reflective surface 12 b, and then part of the light isdirectly emitted from light emitting window 14 a. The other parts of thelight is reflected by the mirror 13 and is emitted from the lightemitting window 14 a. On the base material 5, a long and narrow lightemitting area IA extending in the front/back directions of FIG. 7 isformed.

Also in this embodiment, in the discharge lamp 11, the straight lineformed by connecting the pair of electrodes is located along the opticalaxis C of the reflector 12. The electrodes are provided so as to facethe opening of the reflector 12 of the discharge lamp 11. For thisreason, light which is emitted from the discharge lamp 11 is notdirectly irradiated to the light exposed face (material face), so thatmost of the light emitted from the discharge lamp 11 becomes parallellight when it is reflected on the reflector 12. Therefore, when as thereflector 12, a deposition mirror which reflects light with shortwavelength, but transmits light with long wavelengths in a range of avisible region to an infrared region which does not contribute thecuring of the ink, is provided, it is possible to prevent lightunnecessary for curing the ink, from being irradiated onto the basematerial 5. Furthermore, if a filter which cuts light with a wavelengthof 300 nm or less is inserted in the light emitting side of the lightsource section 10, it is possible to prevent the light with wavelengthsof 300 nanometers (nm) or less from being irradiated on the basematerial 5.

In the ink jet printer, as described above, when the head section 1 aequipped with the ink jet head 4 and the light emitting units 6 and 7,moves above the base material 5 in the state where the ultra-highpressure mercury lamp 11 is lit, the light from a lamp 11 is formed onthe base material 5 so as to be a linear light emitting area extendingin a direction (perpendicular to the face of FIG. 7) which is orthogonalto the direction of movement of the head section 1 a, so that theultraviolet curing type ink is immediately hardened after reaching thebase material 5. As mentioned above, since the component of light withthe wavelength of 300 nm or less is hardly contained in the lightemitted from the ultra-high pressure mercury lamp, even if the basematerial is one that is deformed when it is heated by absorbing lightwith the wavelength of 300 nm or less, it is possible to performprinting or formation of a circuit pattern while preventing deformationof the base material. In addition, since an ultra-high pressure mercurylamp is a short arc discharge lamp so that its is high, light with ahigh peak irradiance can be irradiated to the ultraviolet curing typeink which has reached the base material 5, whereby the ultravioletcuring type ink is promptly hardened (photo polymerization) afterreaching the base material 5, so that it is possible to shorten thecuring time. Therefore, it is possible to prevent deterioration of a dotshape with age, so that it is possible to certainly form an image withhigh quality or patterns of a circuit.

The preceding description has been presented only to illustrate anddescribe exemplary embodiments of the present printer. It is notintended to be exhaustive or to limit the invention to any precise formdisclosed. It will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope. Therefore, it is intended that the invention not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the claims. Theinvention may be practiced otherwise than is specifically explained andillustrated without departing from its spirit or scope.

1. A printer with which an image is formed by discharging a light curingtype ink from a recording head on a recording medium and irradiatinglight from a light emission unit so as to harden the ink, comprising: ashort arc type discharge lamp in which a pair of electrodes is providedin an electric discharge container so as to face each other; a reflectorwhich is provided so as to surround the discharge lamp, which has aconcave face which reflect light from the discharge lamp; wherein thepair of the electrodes are arranged so that a straight line formed byconnecting the pair of electrodes, extends along an optical axis of thereflector, and wherein mercury of 0.08-0.30 mg/mm³, rare gas, andhalogen is enclosed in the electric discharge container and a distancebetween electrodes is 0.5-2.0 mm.
 2. The printer according to claim 1,further including a mirror which forms light reflected by the reflectorso as to be in a linear shape, wherein the discharge lamp is arranged sothat the straight line formed by connecting the pair of electrodes to beperpendicular to the recording medium.
 3. The printer according to claim1, further including a first mirror which changes a direction of lightreflected by the reflector and a second mirror which forms lightdirected by the first mirror so as to be in a linear shape, wherein thedischarge lamp is arranged so that the straight line formed byconnecting the pair of electrodes to be parallel to the recordingmedium.
 4. The printer according to claim 1, wherein the reflector is adeposition mirror which reflects light with short wavelengths, buttransmits light with long wavelengths in a range of a visible region toan infrared region which does not contribute curing of the ink.
 5. Theprinter according to claim 1, wherein the light emitting unit include afirst light emitting unit and a second light emitting unit.
 6. Theprinter according to claim 5, wherein the first and second lightemitting units are provided in both sides of the recording head inmoving directions thereof.
 7. The printer according to claim 6, whereinthe recording head is moved first and second directions.
 8. The printeraccording to claim 7, wherein when printing is performed to therecording medium while the recording head moves toward the firstdirection, ink from the recording head 4 is hardened by light from thefirst light emitting unit, and when printing is performed to therecording medium while the recording head moves toward the seconddirection, ink from the recording head is hardened by light from thesecond light emitting unit.
 9. The printer according to claim 1, whereinthe reflector is a parabola mirror which has a reflective surface in ashape of revolution paraboloid whose center is an optical axis of thereflector.
 10. The printer according to claim 1, further including acarriage on which the recording head and the light emitting unit areprovided.
 11. The printer according to claim 1, wherein the recordinghead has a nozzle which discharges a ink droplet onto the recordingmedium.